1. Field of the Invention
The present invention relates to a coating apparatus for applying a liquid coating material in stripe form onto a thin film that travels in a predetermined direction.
2. Description of the Prior Art
For the application of a coating material onto various types of photographic films, magnetic tapes, photographic paper, or other thin films, a variety of coating methods are now available, each chosen depending on the purpose for which it is used. The methods include one disclosed in Japanese Patent Publication No. 4471/1990 (corresponding to U.S. application Ser. No. 07/428,515, now U.S. Pat. No. 5,045,358) which is known as one of the most efficient coating methods especially for performing stripe coating.
According to this coating method, as shown in FIG. 9, while a film 101 is traveling in a fixed direction, a coating material nozzle comprising a pair of block-like applicator dies 102 and 103 is kept in contact with the film and coating material is discharged through a plurality of coating material discharge ports 105 formed and arranged on the end of the nozzle, so that liquid coating material is applied in stripe form onto the film 101.
On the assembled block-like applicator dies 102 and 103 there is formed a lip portion 108 that protrudes forward to make contact with the film 101. Further, within the assembled applicator dies 102 and 103 there is formed a chamber that serves as a coating material reservoir 106. Coating material is supplied into this chamber 106 from a supply unit (not shown) provided independently of the nozzle 104, being temporarily stored in the chamber. The coating material is discharged from the coating material reservoir 106 through a flow groove 107 and out of the coating material discharge ports 105. The coating material discharge ports 105 are provided in the bottom surface of each of a plurality of applicator grooves 109 which are formed in the end surface 110 forming the lip portion 108. The applicator grooves 109 are provided in the end surface 110 of the lip portion 108 so as to extend in the traveling direction of the film 101 and are positioned at equal intervals in the widthwise direction of the film 101. The lip portion end surface 110 having the applicator grooves 109 thereon is formed as a curved surface with a constant curvature and the nozzle 104 is urged against the film 101 so that the film 101 will travel along the curved surface, whereby the film 101 itself will remain in contact with the nozzle 104 constantly and positively by virtue of the film tension, whereby the applied coating material will have a constant thickness and shape on the film 101.
However, the above-described prior art apparatus has the following problems. Since the film 101 travels while remaining in contact with the lip portion end surface 110 at a certain surface pressure, dust and film residues adhering to the film 101 will adhere to and accumulate on the end surface 110, causing irregularities to be formed on the lip portion end surface 110 that has been formed as a smooth curved surface. This makes it difficult to keep the film 101 in constant and positive contact with the lip portion end surface 110, adversely affecting the layer of coating material applied onto the film, especially with respect to layer-thickness accuracy. In particular, when the length of the film 101 exceeds approximately 1000 m, the resulting irregularities are remarkably increased so as to cause a coating failure.